Most geothermal wells produce heat energy in hot water at temperatures at 300.degree. to 480.degree. F., which are much lower temperatures than used in modern efficient steam electric plants. The overall efficiencies of wet geothermal steam plants are in the range of 10 to 14 percent as compared to fossil or nuclear plants which are in excess of 40 percent.
In the present state of the art, wet steam processes function inefficiently at these low temperatures by flashing through pressure drop 10 to 15 percent of their brine to an impure saturated steam or by using an independent secondary low boiling working fluid for power generation. Large quantitites of residual brine must be circulated and disposed of by ecologically acceptable means. Often the steam-spent brines are repressurized and pumped back into the earth, there being no other practical way of disposal. When steam is released by flashing geothermal brine, the steam produced is in a low temperature range where ordinary steam turbines do not operate efficiently.
Most of the geothermal brines and low pressure steam contain toxic and corrosive non-condensible gases, such as hydrogen sulfide, ammonia, sulfur dioxide, carbon dioxide, methane and ethane, which ultimately escape to the immediate atmosphere and constitute a difficult collecting problem and health hazard. The problem is intensified with the addition of each new well added, ultimately restricting the number of wells in a given geothermal field.
Prior disclosures relating to the conversion of saline water to fresh water include U.S. Pat. Nos. 3,951,752 and 4,054,493. These patents disclose the prior removal of chemical precipitation means those chemical ions present that will form scale on heat transfer surfaces during the flash evaporation stages required to separate salts from saline water and thus produce pure water. To accomplish this a number of chemicals, such as, sulfuric acid, lime, sodium sulfite, carbon dioxide, magnesium hydroxide, ahydride, etc., are metered into the saline water in controlled amounts along with steam at various degrees of temperature to produce the proper insoluble precipitates that are removed in the thermo precipitation tank. This tank is a low pressure tank where the insoluble precipitates are removed by settling and gravity from the water. At least 60 percent of the equipment disclosed in each of these patents is required to accomplish this one objective.
In these two patents, the techniques described must be under chemical laboratory control and analysis at all times to provide the proper amounts and types of chemicals. Also, to remove the soluble gases present in the saline water, a vessel called a deaerator is required. In normal practice this involves the use of steam, vacuum and special chemicals to accomplish degasification.